1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor substrate used for a solid-state imaging device.
The present invention also relates to a method of manufacturing a solid-state imaging device using the semiconductor substrate manufactured by the above method.
2. Description of the Related Art
In general, a Czochralski (CZ) substrate grown by a Czochralski (CZ) method, a magnetic field applied czochralski (MCZ) substrate grown by a magnetic field applied Czochralski (MCZ) method, and an epitaxial semiconductor substrate obtained by forming an epitaxial layer on the CZ substrate or the MCZ substrate are frequently used as a semiconductor substrate used to form a semiconductor device such as a solid-state imaging device or the like.
Especially, the epitaxial semiconductor substrate and the MCZ substrate are mainly employed as substrates for the solid-state imaging devices in order to reduce unevenness of the image contrast resulting from unevenness of a dopant concentration (striation). Since in the epitaxial semiconductor substrate of the epitaxial semiconductor substrate and the MCZ substrate a low-resistance region (e.g., a buried region or a low-resistance substrate) can be formed below a device forming layer, the epitaxial semiconductor substrate is effective in low power drive and lower consumed power and hence the fields of its application are expected to be wider.
When a silicon epitaxial semiconductor substrate is manufactured, a chemical vapor deposition (CVD) method is employed as a practical method and the following four main source gasses are employed.
Two kinds of source gasses, i.e., SiCl.sub.4 SiCl.sub.4 +2H.sub.2 .fwdarw.Si+4HCl! and SiHCl.sub.3 SiHCl.sub.3 +H.sub.2 .fwdarw.Si+3HCl! are employed in a hydrogen reduction method.
Two kinds of source gasses, i.e., SiH.sub.2 Cl.sub.2 SiH.sub.2 Cl.sub.2 .fwdarw.Si+2HCl! and SiH.sub.4 SiH.sub.4 .fwdarw.Si+2H.sub.2 ! are employed in a thermal cracking process.
Of the above four source gasses, the source gas of SiHCl.sub.3 is inexpensive and fast in growth speed and hence is suitable for use in the growth of a thick-film epitaxial layer. Therefore, the source gas of SiHCl.sub.3 is employed to form an epitaxial layer for manufacturing the solid-state imaging device.
However, the epitaxial layer formed by using the source gas of SiHCl.sub.3 has many metal impurities (especially heavy metal impurities) mixed therein during the epitaxial growth thereof and hence it is impossible to sufficiently reduce a white-point defect causing a dark current of the solid-state imaging device, which is a bar to obtain satisfactory characteristics and satisfactory yield.
A source for generating the heavy metal impurity can be considered to be an SUS system member in a belljar of an epitaxial growth apparatus, a source gas pipe or the like. If a source gas contains a material of the chlorine (Cl) system, then it can be considered that the HCl is produced upon the epitaxial growth because of decomposition of the material and then corrodes the SUS system member and hence the corroded material is contained as chloride in the source gas and further mixed into the epitaxial layer.